I discovered that when the 10x optical lens is covered and if you zoom in 10 times. The image does not go dark.
The periscope only activates starting 15x zoom so I believe the 10x optical zoom switches to 10x digital when the periscope is covered.
Similarly the 3x optical switches to digital if the telephoto lens is covered and can zoom digitally upto 9.9x however if the telephoto is covered, the periscope lens ceases to function independently to zoom any further as both telephoto lenses work simultaneously.
The camera system on this phone is not only extensive but it is also quite complex.
